Non-metallic resistance element and process of making same



UNITED STATES PATENT o FICE.

ALEXANDER L. FEILD, or LAKEWOOD, 01110, Assrdnon 'ro 'NArIoNAL cmon comrm, mo, A oonrom'rron OF NEW YORK.

NON-METALLIC. RESISTANCE ELEMENT AND PROCESS OE MAKING SAME.

No Drawing. Continuation of filed June 16, 1919.

To all whom it may concern:

Be it known that I, ALEXANDER L. FEILD, a citizen of the United States, residing at Lakewood, in the county of Cuyahoga and State of Ohio, have invented certain newand useful Improvements in. Non-Metallic Resistance Elements and Processes of Making Same, of which the following is a specification.

This invention relates to refractory, non; oxidlzing, non-metallic, electric resistance elements and to processes of making the same. The invention will be described by reference to a specific illustrative embodiment thereof, it bein understood that the invention is not restricted to the manipulative details hereinafter recited; nor is it -re stricted to the particular ingredients or pro portions of ingredients specified by way of example, inasmuch as these may be varied according to the specific resistance and other properties to'be imparted to the product for special uses in the electric arts.

In its preferred embodiment my novel resistance element is produced by the mutual reaction, at high temperatures and in.a preformed or shaped body, of titanium or a compound thereof, preferably a. compound conslsting of or containing titanium in reduced' or partially reduced state; a refractory oxid or oxid-mixture, preferably consisting of or containing a material proportion of zirconium oxid; and' phosphoric acid; or their equivalents In addition to these components I may use boric acid or its .anhydrid or equivalent materials capable of serving as a flux to promote the proper sintering of the product.

An illustrative embodiment of my inventionis as follows I first prepare amix consisting for example of Titanium carbid 25 parts Zirconium oxid 73 Boric anhhy'drid 2' The above materials, preferably groundto pass a 200 mesh screen, are intimately mixed and compounded with phosphoric acid. The resultin dough should be of proper consistence or extruding in a press or otherwise shaping into a rod or other desired'form of element. For example I have Specification of Letters Patent.

application Serial No. 266,703, filed December 14, 1918. This application Serial No. 304,634.

found it satisfactory to incorporate with approximately 9 kg. of the above mixture about 900 c. c. of 35% phosphoric acid, the resulting mix being then extruded into rods in a hydraulic press at approximately 1000 lbs. .gage pressure. The titanium carbid may be the commercial product known by that name, containing more or less combined nitrogen and the zirconium oxid may be the crude commercial material, or themineral zirkite', containing usually some 5l5% of other oxids, such as oxids of silicon, alumin um, iron, titanium, etc. The proportion of flux may vary, but it does not usually exc'eed 8% of the dry mix. The boric anhydrid may be partly or wholly replaced by other suitable fluxes, including such materials as powderedv glass, silica, borax, the

alkali earth metals, etc.

The shaped element is then dried or permitted to set. This setting occurs spontaneously in the course of a few hours, or may be hastened by heating in oacuo or otherwise, resulting in a hard, firm body which can be handled without danger of deformation. This setting is, probably associated with a chemical reaction between the" phosphoric acid and the oxid components of the mixture,

silicates and phosphates of the alkali or" possibly with the formation of a zirconium prevent the present or subsequent development of flaws or cracks in the articles, and I now regard it as preferable that they should be baked on a rather slow schedule: For instance I have obtained excellentresults by heating the articles in the course of 8-10 hours to about. 600 0., and then allowing them to cool suflicientlyto permit them to be handled. Obviously this procedure will be modified as 'may be required in order properly to anneal the articles, and to avoid tendency to the formation of flaws or cracks in the high temperature treatment next described. In some cases this intermediate 7 Y tering occurs. For a bath of the' composi- "15 tion mentioned above I prefer a tem erature approximately 17251 7 50 O. ile my invention is not limited to any specific conditions for performing this operation, I have found it satisfactory to cause the element in rod or other form to progress regularly through a carbon or graphite tube heated in an electric furnace to the temperathe size of the articles.

ture specified above, the tubes or the rods bein preferably slowly rotated in order to e ua i ze the heating effect. The duration 0 the heating will of course depend upon A material coni traction or shrinkage of the article occurs durin this heating, and it is important,

wthatt e heat should be evenly applied in order toequalizethiscontraction and avoid the development of flaws; also the application of heat should be continued until adherent electroplateof copper .or other theshrinkage is practically complete. It is within my lnvention to anneal or otherwise heat-treat thearticles in any Way in order to insure freedom from flaws.

Resistance elements prepared as above described possess many novel physical and electrical properties, some of which are as follows:

. The element is extremely hard, readilyscratching glass, is very' 'strong, is apparently free from crystalline structure, is capable of receiving an almost metal-like polish, and gives out a clear, musical note or ring. when struck. It easily receives an metal, which permits the electrical connections to be readily made. It is for practical-purposes non-oxidizable in air: for ex- [am Is elements thus repared have been maintained at 500 C. in air for fifty hours poses be regarded as zero, 'although in some without impairment by oxidation or otherwise. The apparent density is in the neigh- ,borhood of 4.0 to- 4.5. The temperature resistance coeflicient may for practical purcases a very small temperature resistance I: been observed;

coefiicient, positive in sign, and of the order of 0.00.0004. per centigrade degree has The specific resistance of'an element compounded from' the particular mix described --above is-of t lie order of'0.03 ohms per cubic ,centimeter, being therefore materially greater than that of the known resistors having a carbon base- Such. a resistor in the form of a rod 10.5 centimeters in length and 1.2 centimeters in diameter, radiating in still air at 25 C., is capable of dissipating electrical energy corresponding to 40 watts with the utilization of a current of only 15 amperes, as compared with 600 ameres for nichrome under like conditions.

'lhe resistance ma however, be varied within wide limits y varying the proportion of titanium carbid to zirconium oxid in the mix, the resistance increasing with increasing proportions of zirconium oxid. I I .now preferthat the zirconium oxid or its equivalents should always predominate in" the mix over .the titan1um carbid or its equivalents, the preferred range of titanium carbid being between 5 and 40% by weight of the dry mix. However my invention is not limited to any particular relative proportions of these components.

The chemical composition of-the fully sintered resistance elements is not now certainly known, although it has been found to contain titanium and zirconium in substantially the relative proportions in which they were introduced into the mix. During the final heating the phosphoric acid undergoes. at least partial reduction, as clearly evidenced by the presence of elemental phosphorus in the furnace vapors, and it is thought that the presence of these vapors or equivalent material having reducing properties is a factor in the production of an element having the optimum texture and physical and electrical properties. It is believed also that the titanium or titanium carbid undergoes at least partial oxidation, 7

wholly or in part to the sesquioxid, Ti O' Without thereb restricting the invention, it is now regar ed as probable that the finished article is essentially a solid solution of these highly refractory oxids, possibly in conjuction with non-oxid compounds of the metals present. r

I have likewise prepared resistance elements by the use in conjunction with titanium carbid of refractory, oxids other than zirconium oxid, and my invention is there- L.

fore not restricted to the employment of this particular oxid, which, however,'I now regard as the preferred-oxid component. For example instead of zirconia I have em-.

ployed double-oxids of the sillimanite t pe 1 (Al SiO) and of the spinel type gO A1 6 Beryl has also been used.

Nor do I desire to restrict my invention to the use of titanium, since iii? probable that other metalsof the same group may be i;

related groups more readily unite to form solid solutions. Thus thorium oxid or mixtures rich 1n this oxld may replace zlrconium oxid. Hence I deslre to cover broadly such .materials as may be the equivalents of titanium carbid and zirconium oxid for the specific purposes of this invention.

This application is a continuation of my .copending application Serial No. 266,703,

filed Dec. 14, 1918.

I claim:

1. A Iron-oxidizing, non-mfetallic electric resistance element having a substantially zero temperature resistance coefficient.

2. An electric resistance element containing a compound of a metal of the titaniumzlrconium group, and a refractory oxid, said element having a substantially zero temperature resistance coefiicient.

3. An electric resistance element containing oxygen compounds of a plurality of elements of the titanium-zirconium group, said element having a substantially zero temperature resistance coeiiicient.

4. An electric resistance element containing titanium and zirconium.

5. An electric resistance element containing areaction product of titanium in reduced state and a refractory oxid. 4

6. An electric resistance element containing a reaction product of titanium in reduced state and zirconium oxid.

7 An electric resistance element containing a reaction product of titanium in reducied state, zirconium oxid and phosphoric aci o 8. An electric resistance element comprising the product of reaction at a sintering temperature of a shaped mixture containing a plurality of elements of the titanium-zirconium' group.

9. An electric resistance element compris ing the product of reaction at a sintering temperature of a, shaped mixture containing titanium in reduced state and a refractory oxid.

10. An electric resistance element comprising the product of reaction at a sintering temperature of a shaped mixture containingdtitanium in reduced state and zirconium 0x1 11. An electric resistance element comprising theproduct ofsreaction at a sintering temperature of a shaped mixture containing titanium in reducedstate, zirconium oxid and phosphoric acid.

12. Process of making an electric resistance element comprising shaping a mixture containing a plurality of elements of the titanium-zirconium group, and sintering the shaped article.

13. Process of making an electric resistance element comprising shaping a mixture containing titanium in reduced state, and a reflractory oxid, and sintering the shaped artic e.

c 14. Process of maln'ng an electric resistance element comprising shaping a mixture containing titanium in reduced state, and zir- COI1lll1In oxid, and sintering the shaped artic e. r

15 Process of making an electric resistance element comprising shaping a mixture containing titanium in reduced state, zirconium oxid, and phosphoric acid, and sintering the shaped article.

16. Process of making an electric resistance element comprising shaping a mixture containing titanium c'arbid, zirconium oxid and phosphoric acid, and sintering the shaped article. p 17. Process of making ,an electric resistance element comprising shaping a mixture containing titanium carhid, zirconium oxid, phosphoric acid, and a flux, and sintering the shaped article;

18. Process of making an electric resistance element comprising shaping a mixture containing titanium carbid, zirconium oxid,

, phosphoric acid, and an oxid of boron, and

sintering the shaped article.

In testimony whereof, I aflix my signature.

) ALEXANDER L. FEILD; 

